The dye-sensitized solar cell is also referred to as a wet solar cell, a Graetzel cell, or the like, and is characterized by having an electrochemical cell structure as typified by an iodine solution without using a silicon semiconductor. In general, the dye-sensitized solar cell has a simple structure in which an iodine solution or the like is disposed as an electrolyte solution between a porous semiconductor layer, such as a titania layer, formed by baking titanium dioxide powder or the like onto a transparent conductive glass plate (a transparent substrate having a transparent conductive film laminated thereon) and making a dye adsorbed onto the baked powder, and a counter electrode composed of a conductive glass plate (conductive substrate).
The electrical generation mechanism of the dye-sensitized solar cell is as follows:
A dye adsorbed to the porous semiconductor layer absorbs light entering from a surface of a transparent conductive glass plate which is a light-receiving surface, thus causing electron excitation. Electrons thus excited migrate to a semiconductor and are introduced to the conductive glass. Then, electrons having returned to a counter electrode are introduced to the dye stripped of electrons through an electrolytic solution, such as iodine, thus reproducing the dye.
The dye-sensitized solar cell is inexpensive in terms of the materials thereof and does not need a large-scaled facility for its fabrication, thus attracting attention as a low-cost solar cell. For the purpose of further cost reduction, a study is being made, for example, to exclude the expensive transparent conductive film.
One example of a method for excluding the transparent conductive film is to provide wiring made of conductive metal in place of the transparent conductive film present on a glass surface. In this case, however, part of incident light is blocked by the metal wiring, thus involving efficiency degradation.
As means for making improvements in this regard, there is disclosed a photoelectric conversion element (see Patent Literature 1) in which a dye-carrying semiconductor layer, for example, is formed on a transparent substrate having no transparent conductive films which is a light irradiation side, and a perforated collecting electrode is arranged on the dye-carrying semiconductor layer. The patent literature states that the perforated collecting electrode has a net-like or grid-like structure, and that this collecting electrode is placed on a coated film of a porous semiconductor substrate and calcined at 500° C. for 30 minutes.
In addition, there is disclosed, for example, a photoelectric conversion device in which a collecting electrode is made linear, mesh-like or porous (see Patent Literature 2). Note however that Patent Literature 2 does not mention either any specific porous structures or any methods for fabricating the porous structures in regard to making the collecting electrode porous.